In general, plants store energy in starch, and the starch may be stored in grain, beans, tubers, or the like. Since these natural sources of starch are cheap and abundant all over the earth, it has been applied to various industrial applications, including the food, paper, textile, and glue industries. Native starch refers to partially crystallized nano-level particles. Hydrogen bonds between these particles make them assemble with each other to become a huge assembly. Therefore, it is difficult for the native starch to be used in a melting process. Conventionally, starch is often used as filler in plastics to decrease cost and increase rigidity.
The hydrogen bonds between starch particles may be broken by adding polyol into the starch. The polyol may be glycerol, sorbitol, or polyethylene oxide (PEO), for example. As a result, the molecular chain entanglement and chain motion of the starch can reach a point where the starch develops characteristics of thermoplasticity. Thus, the thermoplastic starch may have a mobility similar to that of other synthesized polymers, and therefore it may be suitable for use in molding and extruding the thermoplastic. However, pure thermoplastic starch has poor mechanical strength, resulting in limited applications. Therefore, a mixture of thermoplastic starch and a biodegradable polymer, or a mixture of thermoplastic starch and polyolefin may be used.
In Taiwan, over 1.5 million tons of plastic material is used every year. If all this plastic material could be replaced with an eco-friendly material (biomass content 25%), consumption of the petroleum-based material could be reduced by about 400,000 tons per year.
In addition, in some applications such as automobile interiors, domestic electrical devices, or electronic products, the plastic material needs to be flame-retardant. However, since thermoplastic starch itself is inflammable and exhibits melt-dripping behavior, it is very difficult to develop a flame-retardant starch-based bio-composite. Thus, petrol materials with high impact resistance, such as polystyrene, acrylonitrile butadiene styrene (ABS), polycarbonate (PC)/ABS, are still the most commonly used plastic materials.
Therefore, a novel thermoplastic starch and bio-composite with flame-retardant properties is required.